Various types of crane camera systems have been proposed to enable the crane operator to see conditions around the crane arm or around the load being worked by the crane. For example, U.S. Pat. Nos. 6,894,621 and 6,744,372, and U.S. Published Application 2004/0026348 disclose providing displays in the crane cab of videocam images from one or more cameras mounted on the trolley of an overhead crane and/or on the hook or hoist device, along with other safety sensors, such as for detecting wind gusts or the proximity of obstructions. U.S. Pat. No. 6,985,085 discloses providing a remote-controllable and steerable camera on the boom of a crane for imaging the vicinity of the load. U.S. Pat. No. 6,880,712 discloses look-down sensors on the trolley of an overhead-type crane for detecting the corners of a load. U.S. Pat. No. 3,881,608 teaches the use of sensors on a overhead crane boom to detect the trolley position. U.S. Pat. Nos. 6,894,621 and 6,351,720 and U.S. Published Applications 2005/0192732, 2005/0232733, 2004/0026348, and 2004/0149056 also disclose various systems of cameras or sensors provided on the trolley to detect the position of the load.
However, these prior systems have not provided for reliably transmitting video signals to the crane operator while working around various types of obstructions typically encountered on a work site. If the video signals are carried by a wire cable or optical fiber cable, then the range of motion of the moving video camera may be limited by the wired connection. If wireless transmission is used, then for high-frequency (MW) signals, line-of-sight transmission between the hook and the operator cabin must be maintained despite obstacles on the worksite and the constant motion of the hook to the operator cabin. If low-frequency (RF) signals are used, then the data rate that can be transmitted is reduced and/or the image resolution must be lowered, and signal transmission may deteriorated by obstructions on the work site.